1. Field of the Invention
The present invention relates to a visible light communication (VLC) system. More particularly, the present invention relates to an apparatus and a method for arranging communication links respective to a wireless peripheral device using visible light communication as media.
2. Description of the Related Art
The luminous efficiency of a Light Emitting Diode (LED) has improved in recent days and the cost thereof has also dropped, thus increasing the demand for LED lighting. LED are now popular in the generalized lighting market, such as the market for fluorescent lamps, incandescent lamps, etc., as well as the specialty lighting market, such as the market for special lights used in mobile devices, a displays, vehicles, a traffic signals, and advertising boards, etc. Particularly, while the luminous efficiency of a white LED is already greater than the efficiency of an incandescent lamp, products superior even to a fluorescent lamp have also come out. Moreover, due to depletion of a Radio Frequency (RF) band frequency, confusion possibility between various wireless communication technologies, increase of demands for security, advent of a super-speed ubiquitous communications environment in 4th generation wireless technology, etc., interest in light—wireless (radio over fiber) technology complementary with an RF technology has recently increased. Therefore, research about the visible light wireless communication has progressed in various enterprises, research institutes, etc.
In a case of a portable mobile device, such as a cellular phone and a Personal Digital Assistant (PDA), and a small-sized digital product, such as a digital camera or an MPeg audio layer 3(MP3) player, present research has been focused on peripheral interfaces performing communication between devices by mounting an Infrared Data Association (IrDA) module based on infrared rays. Also, related goods have been developed and commercialized. Infrared ray wireless communication, which is distinguishable from RF communication, such as a Bluetooth or a Zigbee. etc., as infrared wireless communication operates without confusion between devices, has security, and can be implemented with low power.
As wireless communication technology has been developed, there has been suggestion to eliminate an IrDA module in a method for performing communication between devices by using a infrared LED. There is an advantage in using an LED for providing visible light in peripheral interface communication in that a user can check the communication path with his/her naked eye, in order to identify communication security. Moreover, since it is easier to know whether the user is in a proper communication path, a diffusion angle of light can be reduced in comparison with conventional infrared communication, so that high-speed communication or low power driving can be implemented.
Therefore, systems using visible light will likely remain predominant in a market for short-distance wireless communications systems for the foreseeable future.
FIG. 1 is a view illustrating a process for searching for outer infrared communication devices in a conventional infrared communication, in which the process is shown according to a sequence of time slots.
With reference to FIG. 1, a transmitting side device (primary) beginning to perform an initial infrared communication transmits a first exchange identification (XID) (A, 0) in order to check the exact number of receiving side devices (secondaries) for performing communication with the primary.
Once the number of the secondary devices receiving the transmitted frame is checked, the primary device determines numbers equal to the number of the checked secondary devices so as to allow the secondary devices receiving a first XID (A, 0) frame to perform a random selection of one of determined numbers. For example, if the number of the checked secondary devices is five, the numbers from 0 to 4 are determined, and the checked secondary devices randomly select one of the numbers from 0 to 4.
According to such a scheme, secondary devices, the number of which is “m”, randomly select one among the numbers from m to 1.
Then, if an XID (n) frame (herein, n defined as a value, which is bigger than 0 and is smaller than m−1.) among the XID frames, which are transmitted from the primary device according to predetermined time slot, is transmitted to the secondary device, the secondary device selecting “n” among the numbers from m to 1 receives the XID (n) frame so as to transmit an XID response frame in nth slot time to the primary device again.
If at least two secondary devices select the same number and transmit an XID response to the primary device in the same time slot, such a scheme is repeatedly performed by generating a random number until another time slot is selected, through this scheme, it is possible to find out all corresponding secondary devices while avoiding confusion between the secondary devices, the number of which can be plural.
However, in a case of the above-described infrared communication, when a frame searching for an outer infrared communication device, i.e. a device discovery frame, is performed, the length of the device discovery frame is shorter in comparison with one allocated time slot. Therefore, when frame transmission is completed, there is a problem in that the visibility decreases until a frame of the next time slot begins. When the device discovery frame utilizing infrared communication is applied to visible light communication (VLC), there is a problem in that visibility of the communication links decreases in a device discovery procedure, so that the user can not arrange the communication links while watching visible light by his/her eye.